The present invention relates to a process and apparatus for producing steel by joining different components or different grades of steel.
Centuries ago, in the Near East, blades for knives and swords with amazing properties such as, for example, so-called damascene swords, were manufactured. The success and fame of these blades was not as a result of the patterned appearance but rather of their properties inasmuch as the swords combined the greatest hardness with a high degree of toughness thereby making them unsurpassable as steel for tools and arms. Damascene swords apparently supposedly consisted of two different steels, one of which had a greater hardness, and the other a better toughness with both steel components being elaborately "interwoven" or closely joined with one another.
Centuries ago the art of manufacturing damascene swords was lost; however, even if such art could be known again, the process then in use could not be applied for industrial production today and, consequently, would be of no economic value.
During the last century, there was a similar material developed, a so-called puddled steel which also exhibited excellent properties for blades of knives and arms. However, metalurgists today consider the steel as being disadventageous because it is interspersed with slags in a very irregular manner. However, such blades for knives and arms also had excellent cutting ability and those who may still possess knives made from a puddled steel except the endless cleaning rather than exchange these knives having excellent cutting abilities, for modern knives, i.e., knives with stainless steel blades.
The present invention essentially resides in providing a process and apparatus for a production of steel by joining different components, i.e., different grades of steel and/or alloying constituants so that steel with never changing properties and optimum toughness having an excellent hardness can be industrially manufactured.
In accordance with advantageous features of the process of the present invention, one or several solid state materials or components are fed into a liquid melt consisting essentially of one or more components, with the solid state material or materials being only melted on a near surface but not melted open in the temperature of the liquid melt which is preferably only slightly higher than the temperature of the liquidus, and with the material produced in such a manner being made to freeze or solidify and undergo subsequent conversion and, if necessary, heat treatment.
In accordance with further advantageous features of the process of the present invention, the casting temperature is that much above the otherwise common temperature that the quantity of heat of the liquid melt to respectively melt the solid state material. Advantageously, the solid components may be blown into the melt with the blowing-in being effected by an inert gas as a carrier gas such as, for example, argon.
It is also possible in accordance with the present invention for the blowing-in of the solid material ingredients to be carried out by means of an active gas such as, for example, nitrogen or carbon monoxide, or by a mixed gas.
The solid component or solid components may, in accordance with the present invention, be pressed into the liquid melt and the solid material ingredients may be fed in the form of granulates or balls into the liquid melt.
Moreover, according to the process of the present invention, the solid material ingredients may be spooled into the liquid melt in the form of wires and, the solid component or solid components may be preheated.
Also, the carrier gas may also be preheated prior to blowing the same into the liquid melt and solid components of different complimentary materials are fed into the liquid melt. It is also possible for the material ingredients of different grain size to be fed into the liquid melt and, advantageously, gravity die temperature may be increased above normal.
Advantageously, in accordance with further features of the process of the present invention, the following typical combinations of material for steel may be provided:
______________________________________ component C Si Mn Cr Ni Mo Nb B ______________________________________ A .05 .10 .40 -- 0.40 -- -- -- .25 .40 1.80 -- 1.80 -- -- -- B .80 .40 .40 .40 max .20 .004 max .80 .40 1.00 2.00 2.00 1.00 0.30 .005 ______________________________________
Advantageously, the material is subjected to a heat treatment of Austenitizing at 880.degree. up to 960.degree. C., chilling in air, oil or water, tempering at temperatures between 160.degree. and 720.degree. C.
In order to achieve a better conductive discharge of the carrier gas, advantageously the head of the ingot is heated.
The grain size of the fed solid state materials is between 1 and 15 mm and, preferably, between 3 and 8 mm. In the process of the present invention the solid state materials, especially the granulates fed into the liquid melt, have a predetermined shape of, for example, a lenticular or long grain shape.
Additionally, the process of the present invention is characterized by the fact that the solid state materials stored during the liquid phase, granulates in particular, as a result of specific measures, show different forms of distribution.
By using the process of the present invention, it is possible to achieve an industrial production of steel which with extreme hardness has a high degree of toughness so as to exhibit the stunning properties of presumably one would have called a "damascene" steel.
Moreover, the process of the present invention makes it possible to "interweave", that is, to closely join one or more components in such a manner that the above-noted excellent properties of the steel can be obtained.
Additionally, with the process of the present invention, the different components are joined at a moment at which one of the component or components is or respectively are still liquid, while the other component or components is or are in a solid state. The result of this is that the particles of the solid component or solid components completely melt on but do not completely melt open. After a freezing or solidifying of the material, a composite structure is formed which has a matrix consisting of the cast steel and embeds numerous metallic segregates from the other component or other components fed in solid form.
If a steel produced by the process of the present invention is rolled out as a slab or the like, the embedded segregates take lamellar shape or the like which means that the combination of a single component becomes even more intimate and, optimal properties can be obtained by a following quenching and tempering treatment which, however, according to the present invention, is not necessary.
By using the process of the present invention, composite steel can be produced which distinguishes itself by its combination of a high degree of firmness and toughness which cannot otherwise be obtained.
Moreover, the welding ability of the steel according to the present invention is substantially better than can be expected because of the high degree of firmness and the cracking resistance is so great that the incipient cracks forming in the hard particles do not continue in the softer matrix but are caught or trapped in it, and this also applies for the formation of cracks induced by hydrogen.
With the process of the present invention, two steels of a great hardness and toughness can be produced and, moreover, the use of the process of the present invention allows the industrial production of materials with special chemical properties as well as industrial production of materials with special wear resistance.
Additionally, no difficulties arise from the industrial production of materials with special magnetic properties with the process of the present invention and, the process of the present invention allows the production of steel which is suitable for military purposes such as, for example, armoured steel.
Furthermore, the process of the present invention permits the production of special cutters or a material with special electrical properties.
By virtue of the fact that the casting temperature is that much above the otherwise common temperature than the quantities of heat of the liquid melt are sufficient to melt on the solid state materials, the quantities of heat from the melt are sufficient to melt on the component or the respective particles.
Additionally, the present invention enables the blowing-in of, for example, the solid state materials into the gravity die or into a steel pouring ladle or into a pouring stream.
Moreover, by employing an inert carrier gas such as, for example, argon, such carrier gas does not change the composition of the liquid material although it is possible to blow in the solid state materials by means of an active gas.
It is also possible in accordance with the present invention to do without carrier gas completely, i.e., if the solid state materials are pressed into the melt.
Likewise, when solid state materials are fed into the melt or in the form granulate or balls, the balls or granulates can be pressed or otherwise brought into the melt through pipes, conduits, and/or borings, with the balls and/or granulates being distributed in the melt by a casting turbulence.
With large quantities of the fed solid, the cooling effect can become so great that, in compensation, the solid state materials and/or the carrier gas as well may be preheated. The freezing or solidifying in the gravity die or the like usually starts from the place of the greater cooling, that is, the side wall of the gravity die and, in the present case, this is supported by the injected solid components, for example, granulate particles thereby altering the cooling conditions.
By mixing several solid state materials such as, for example, granulates, with each other it is possible to cause different properties in the composite homogeneous to the outside and produced with the process according to the present invention.
Different degrees of melting on of the particles may be obtained by providing different grain size components into the liquid melt thereby resulting in a change in the corresponding properties in the finished material.
If, prior to the end of the blowing-in operation or phase, a lid is already formed in the head of the slab of the respective ingots, there is the danger that the blow-in gas cannot escape anymore and form bubbles in the ingot. This premature "freezing" can be counteracted by appropriate measures such as, for example, the use of exothermal or insulating pouring powders or of a heating device for heating the head of the ingot.
The grain size of the solid state materials fed into the melt depends, among other things, upon the available heat content. On the one hand, the injected particles must be completely melted on or welded on to the surface and, on the other hand, they must not completely dissolve while being in the liquid melt. Finally, later in the solid phase, they must not dissolve by diffusion either. The optimal particle size has to be established by test and, therefore, the particles size of between 1 and 15 mm and, preferably between 3 and 8 mm, represent indication of examples for preferential ranges according to the present invention. The solid state materials in the process of the present invention may have shapes that differ from a ball shape and may be formed such as, for example, cut steel shot.
In the edges of the gravity dies, the part of the sheets that that latter will be near the surface, an accumulation of solid particles is desirable and should be caused and this may be achieved, above all, by an appropriate heat conduction of the side wall of the gravity die, a so called fly-paper effect.
In accordance with advantageous features of the apparatus of the present invention, at least one group-teeming bottom plate is provided along with at least one gravity die mounted in an upright position and connected by a channel to a funnel. The group-teeming bottom plate, a channel or several such channels debouch from beneath into the relevant gravity die, and a carrier gas source is provided for feeding a mixture of a carrier gas and solid state materials is joined to the relevant channel and/or in the side wall of the gravity die, at least one boring is made which is joined to a pipe connected to the same or another carrier gas source to feed a mixture of carrier gas and solid state material parts and/or relevant boring is connected with an appropriate conveying device for pressing-in of the solid state material ingredients.
The solid state material ingredients may be fed, in accordance with the apparatus of the present invention, by means of a lance with a fireproof coating to the pouring ladle or during the casting process to a mold or into the pouring stream. By virtue of the features of the apparatus of the present invention, it is possible to feed the solid state materials into the liquid melt and into a gravity die, into a steel pouring ladle or into the pouring stream.
By virtue of the provisions of a lance with a fireproof coating, it is possible to feed the granulates or the like into, for example, a steel pouring ladle, or during the casting process, into a mold. For the blowing-in into a pouring ladle, the granulates or the like will have to be substantially coarser. Due to the longer dwell time in the liquid phase, a greater part of the particles being melted open from the direction of the edges cannot be avoided here.